Field of the Invention
The present invention relates to a parallelogram linkage structure for a scale, in particular a scale operating according to the electromagnetic force compensation principle.
Description of Related Art
Such parallelogram linkage structures are used for guiding a load receiver under load parallel to an as a rule stationary base body. Via a lever assembly coupled to the load receiver, the movement of the load receiver is reduced one or several fold and thus amplified, lastly for metrologically detecting the deflection of a lever or of a magnet arranged thereon or of a coil.
For stability reasons, the two parallel linkages (also referred to as “parallel guide elements” in the following) guiding the load receiver are spaced apart from one another as far as possible in the movement direction Z of the load receiver. The base body projects between these parallel guide elements, in order to form supporting points for the aforementioned lever mechanism there. For high precision scales, this gives rise to the problem of the projecting part of the base body (also known as the “scale bearing”) has limited rigidity. The closer the two parallel guide elements are to one another in the Z direction, the less this rigidity, meaning that the projecting scale bearing can only be configured with correspondingly less height. While spacing the parallel guide elements further apart in the Z direction also allows a correspondingly more strongly dimensioned scale bearing between them, the desired maximum possible compactness of overall dimensions of the parallelogram linkage structure is sacrificed.
In order to ensure a rigid scale bearing of maximum stability between the parallel guide elements, the prior art makes provision for breaching the parallel guide elements within the monolithic structure and for guiding a part of the base body through this breach, also for bracing the projecting part.
DE 32 30 998 C2 discloses the provision of a bearing projection projecting vertically through the bottom parallelogram linkage for forming a lever supporting point. A similar procedure is followed in U.S. Pat. No. 4,100,985 A, but instead of a base body portion, a lever mechanism is guided through the parallelogram linkage here.
DE 20 008 066 U1 shows a monolithic parallelogram linkage structure in which each parallelogram linkage has a centrically formed recess in order to create access for machining tools, without additionally bracing the projecting part of the base body.
DE 197 29 623 B4 shows how an elongate base body is fastened onto a scale frame by means of two screws, wherein the two screws go through an opening in the bottom parallel linkage. Centrically penetrating the parallelogram linkage has the disadvantage of the mount becoming narrow and thus reducing torsional rigidity. A lateral mounting of the projecting part of the base body is proposed in another embodiment of DE 197 29 623 B4. Although the lateral mounting elements make the overall system quite rigid, the width of the necessary installation space likewise increases. In both cases the metrologically sensitive projecting part of the base body is disadvantageously influenced by tightening torques.